Frustoconic anchoring jaws for cables and their methods of manufacture

ABSTRACT

To prepare a split frustoconic jaw intended for the anchoring of a cable, a part is first taken bounded externally by a frustoconic surface and hollowed by a cylindrical axial channel whose inner surface is advantageously striated. This part is sawed into by substantially axial and radial slashes leaving bridges to subsist of small thickness at the bottom of these slashes throughout the central channel. An assembly ring is mounted in an outer annular groove and the whole is subjected to cementation treatment so as to surface harden the jaw while making the bridges fragile.

BACKGROUND OF THE INVENTION

The invention relates to split frustoconic jaws designed for anchoringto retainer blocks cables such as those intended to producepre-stressing in a concrete structure or to brace a bridge, these jawsbeing adapted to grip these cables and to coact with housings have atleast one complementary frustoconic portion, said housings, beinghollowed from one side to the other in said blocks.

The jaws concerned are composed of two, three or four indenticalelements--called "keys" below--each derived from an original partbounded externally by a frustoconic surface and hollowed by acylindrical axial channel whose inner surface is advantageously scored,said original part being decomposed into said keys by sawing along two,three or four radial half-planes.

In known embodiments of the above jaws, the keys obtained by sawing aregathered in bulk.

Then they are subjected to a surface hardening heat treatment, and, toform a jaw, there are taken from the keys thus treated the requirednumber--generally three--of the latter and they are assembled by meansof an annular steel ring housed in a circular groove itself hollowed inthe outer frustoconic surface of the original part, in the vicinity ofits large base.

This assembly formula presents certain drawbacks and in particular thefollowing.

By reason of the mixing in bulk of the keys between their fabrication bysawing and individual taking-up following the hardening treatment, thekeys taken up to constitute each jaw do not generally come from the sameoriginal part.

This circumstance would be of no consequence if all the keys werestrictly identical.

However this is not the case in industrial manufacture on a productionscale since then the saw lines are not always strictly axial and radialand their mutual angular separations are not always strictly equalbetween them.

Thus the cutting out of the original part can present the sinuous shapevisible at S in FIG. 1 or extend along plates inclined to the idealradial planes, as visible at R in FIG. 2.

In this case, the gripping of the jaws concerned does not lead toperfect juxtaposition plane to plane of the lateral surfaces ofcontiguous keys : the juxtaposition of these keys reconstitutes a veryimperfect cylindrical channel, with the formation of excessive andirregular spaces between the keys and possibly the creation of gaps atthe level of their connections, which can generate high local stressescapable of causing the breaking or the slipping of the cables to beanchored.

To overcome this drawback, severe checks and manufacturing tolerancesmust be imposed, hence expensive for the manufacturer of the keys

It is an essential object of the invention to overcome the drawbackindicated in a particularly economical manner since it permits thechecks indicated to be eliminated.

GENERAL DISCRIPTION OF THE INVENTION

Accordingly the anchoring jaws according to the invention areessentially characterized in that the totality of the keys which composeeach of them come from the same original part, the sawing intended todecompose this part into keys being left intentionally incomplete so asto allow connecting bridges of small thickness to subsist betweencontiguous keys along the central channel of said part.

The method of manufacture of said jaws is for its part essentiallycharacterized by the following sequence of operations : sawing of theoriginal part along substantially axial and radial severage linesperformed so as to allow bridges of small thickness to subsist at thebottom of these severage lines along the central channel, said bridgesholding the keys joined to one another and treatment of the part thusslashed adapted to surface harden the keys whilst rendering the bridgesfragile.

In preferred embodiments, recourse is had in addition to one and/otherof the following features:

an assembly ring of steel is mounted in the annular groove of the partafter its sawing and before the hardening treatment,

the bridges have a radial thickness less than or equal to 1 mm,

the inner cylindrical surface of the channel is serrated and the bridgesare discontinuous, being hollowed out radially at the level of thehollows of the serrations.

The invention comprises, apart from these main features, certain otherfeatures which are preferably used at the same time and which will bemore explicitly considered below.

In the following, a preferred embodiment of the invention will describedwith reference to the accompanying drawing given of course asnonlimiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 of this drawing, show respectively in axial section alongthe line I--I FIG. 2, and in end view the blank of a jaw according tothe invention such as it appears after sawing the original part andbefore positioning of the ring.

FIG. 3 shows on a larger scale a portion of FIG. 1.

FIGS. 4 and 5 show respectively in side view and in end view the jawobtained according to the invention from the above blank.

DESCRIPTION OF PREFERRED EMBODIMENTS

To produce such a jaw, a start is made in manner known in itself with apart 1--called "original part" in the present description--boundedexternally by a frustoconic surface 2 and hollowed axially by acylindrical channel 3.

The inner surface of this channel is scored at 4 along particularly ahelicoidal thread with a triangular cross-section.

An annular groove 5 is in addition hollowed in the frustoconic surface 2in the vicinity of its large base.

The part 1 concerned is advantageously constituted of soft steel easilymachinable but which can be surface hardened by heat treatment such ascementation.

It is in this part 1 that the narrow slashes 6 are formed by sawinglying along planes passing through the axis X of said part.

In the preferred embodiment illustrated, these cuts 6 are three innumber and spaced angularly from one another by 120° around the axis X.

The slashes 6 are not integrally hollowed in the part 1: each of them isinterrupted so as to allow to subsist along the central channel 3 abridge 7 throughout this channel.

The radial thickness e of each bridge 7 is very small, being preferablyless than 1 mm, for example of the order of 0.3 to 0.7 mm, when theelements to an anchored by the jaws concerned are strands having adiameter of the order of 15 mm.

The depth of the striae 4 can be greater than said thickness e: thebridges 7 are then interrupted at the level of the hollows of the striae4 by holes 8 (FIG. 3) showing in the form of dots.

It is to be noted that in spite of the smallness of the thickness e, itis relatively easy to adjust the sawing in consequence considering thatthe production of the three slashes 6 can be done simultaneously bymeans of three milling cutters whose respective dimensions and positionsare strictly determined and between which the part 1 is forced axially.

The jaw blank thus slashed remains constituted by a single block of"monolith" and may be mixed in bulk with other simular blanks.

The stresses exerted on the bridges 7 at this stage are in fact verymuch less than those which would be necessary to break said bridges,which have not yet been made fragile by cementation and have thenessentially the purpose of preserving a bond between the keys to beformed 9.

Then one by one the one piece blanks which are not yet divided intoseparate keys are taken up so as to position an assembly ring 10 in eachgroove 5 said ring being generally constituted from spring steel.

The assembly is then subjected to the cementation treatment whichresults in the surface hardening of the keys 9 and of the bridges 7.

This treatment is particularly heating at a temperature comprisedbetween 900° and 1000° C. performed in three-fourths of an hour in acarburising atmosphere, said heating being followed by quenching.

The steel so treated has then become superficially very hard and thebridges have become relatively fragile and breakable.

The simple taking up in the hands of the assembly of this stage sufficesto break said bridges 7, which then become broken into small fragments.

This breakage which only permits the roots 11 of said bridges tosubsist, which roots are comparable to untrimmed burrs, releases theconstituent keys 9 of the jaws with respect to one another.

However this release no longer risks completely separating these keys inview of the presence of the ring 10.

It is to be noted that the presence of the residual burrs 11 isadvantageous considering that at the beginning of the gripping of thejaw these burrs maintain the keys mutually separated from one another,which prevents their dissymmetric angular assembly being manifested bythe creation of too wide a slit.

On the subsequent clamping, these burrs are not troublesome consideringthat they are then crushed and broken forming small chips.

The keys 9 constituting the jaws thus manufactured have the importantadvantage of coming from the same original part so that they arejuxtaposed laterally in intimate contact between complementarycontiguous surfaces, the juxtaposed surfaces having exactly the sameirregularities (sinuosities, defects of orientation, of angularposition, . . .) and that their juxtaposition reconstitutes exactly thedesired cylindrical channel.

This result is obtained even for relatively large irregularitiesobserved on the traces, orientations and positions of the saw lines,which enables the reduction to a considerable extent of the importanceand the cost of checks relating to the sawing operations.

As a result of which, and whatever the embodiment adopted, there isfinally provided an anchoring jaw whose constitution, manufacture andadvantages emerge sufficiently from the foregoing.

As is self-evident, and as emerges besides already from the foregoing,the invention is in no way limited to those of its types of applicationand embodiments which have been more especially envisaged: itencompasses, on the contrary, all modifications, particularly thosewhere the number of bridges 7 subsisting between the keys 9 at the endof the sawing operations would be less by one unit than the number ofcuts 6 effected in the course of the sawing operations, and those where,the bridges being sufficiently thick to ensure provisionally the mutualjoining of the keys even after their hardening, the assembly ring wouldbe mounted on the frustconic part after the hardening treatment and notbefore the latter.

We claim:
 1. Blank for a split frustoconic jaw, said blank constitutedby a part bounded externally by a frustoconic surface and hollowed by acylindrical axial channel with a striated inner surface, said partincluding keys formed radially outwardly of said cylindrical axialchannel by substantially radial slashes and a linking bridge of smallthickness subsisting at a radially inner end of each of said radialslashes and along the central channel.
 2. A blank according to claim 1,wherein each bridge has a radial thickness less than or equal to 1 mm.3. A blank according to claim 1, wherein each bridge is discontinuous,being interrupted at the level of hollows of the striae by holes. 4.Method of manufacturing a split frustoconic jaw intended for anchoring acable comprising the following steps:(a) sawing substantially axiallyand radially extending slashes in an original part to form a blank; (b)allowing bridges of small thicknesses to subsist at a radially inner endof the slashes along a central channel in said blank; (c) holding keysof the blank together by said bridges; (d) hardening the surface of thekeys whilst making the bridges fragile; and (e) breaking the bridgesinto small fragments to form the split frustoconic jaw.
 5. Methodaccording to claim 4, wherein an assembly ring of steel is mounted in anannular groove of the blank after sawing and before hardening.